NJM3775E3 데이터 시트보기 (PDF) - Japan Radio Corporation

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NJM3775E3

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Japan Radio Corporation  

NJM3775

s FUNCTIONAL DESCRIPTION

Each channel of the NJM3775 consists of the following sections: an output H-bridge with four transistors and four

recirculation diodes, capable of driving up to 750 mA continuous current to the motor winding,

a logic section that controls the output transistors, an S-R flip-flop, and a com- parator. The clock-oscillator is

common

to both channels.

Constant current control is achieved by switching the output current to the windings. This is done by sensing the

peak current through the winding via a current-sensing resistor RS, effectively connected in series with the motor

winding. As the current increases, a voltage develops across the sensing resistor, which is fed back to the compa-

rator. At the predetermined level, defined by the voltage at the reference input V , the comparator resets the flip-

R

flop, which turns off the upper output transistor. The turn-off of one channel is independent of the other channel.

The current decreases until the clock oscillator triggers the flip-flops of both channels simultaneously, which turns

on the output transistors again, and the cycle is repeated.

To prevent erroneous switching due to switching transients at turn-on, the

NJM3775 includes a digital filter. The clock oscillator provides a blanking pulse which is used for digital filtering of

the voltage transient across the current sensing resistor during turn-on.

The current paths during turn-on, turn-off and phase shift are shown in figure 3.

V MM

1

2

3

RS

Motor Current

1

2

3

Fast Current Decay

Slow Current Decay

Time

Figure 3. Output stage with current paths

during turn-on, turn-off and phase shift.

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